Inlet or exhaust line for a reciprocating machine

ABSTRACT

An inlet or exhaust line for a reciprocating machine attenuates the sound level of the machine while being simple and economical to produce. A sensor measures the instantaneous flow rate of gases passing through the line while a restriction device variably restricts the cross-section of the line as a function of the instantaneous flow rate measured by the sensor. Material for absorbing acoustic energy covers the internal wall of the line.

This application has been filed under 35 USC 371 for the inventiondescribed and claimed in international application numberPCT/FR93/00703, filed Jul. 7, 1993.

The present invention relates to an inlet or exhaust line for areciprocating machine.

According to the invention, by reciprocating machine is meant any devicecreating flow pulsations either in an induced manner or in a spontaneousmanner, such as, for example, a combustion engine, a compressor or aheat pump.

It is known that gas inlet or exhaust pulsations of a reciprocatingmachine are a major source of noise, especially low-frequency noise. Thesame is true for the outputs of all reciprocating machines (compressors,vacuum pumps, heat pumps etc) and for the inlets of these machines.

These pulsations have very high energies at precise frequencies relatedto the cycle of the machine, but are very weak for differentintermediate frequencies.

In fact, acoustic analysis of this noise reveals a spectrum havingdiscrete lines of very high energy.

In order to decrease the level of noise generated by the pulsations of acombustion engine for example, exhaust lines fitted with silencers areused.

However, although these silencers enable the low-frequency pulsations ofthe exhaust gases to be attenuated moderately, they simultaneouslyintroduce into the exhaust line singularities which are manifested byfluctuations and turbulence in the flow, and therefore by noisepossessing medium and high frequencies.

In addition, when an exhaust line is installed on a motor vehicle, itsgeometrical singularities are all the more important as it has to befitted into the space available beneath the vehicle. Thus it isfrequently observed in exhaust lines that the internal cross-section ofthe pipe varies several times from one end of the exhaust line to theother, the exhaust line moreover including many baffles and otherobstacles likely to generate noise.

As a result, the usual exhaust lines, which are constituted by tubularpipes connecting silencers, are relatively bulky and are the source ofadditional blowing noise; furthermore, they lead to quite appreciablepressure drops.

Devices are also known for reducing the noise of an exhaust line whichgenerate, in the direction of the exhaust line, an acoustic wave whichis as strictly as possible equal to that emitted by the latter.

However, such devices are very bulky, require very sensitive electronicand acoustic equipment and, consequently, are not very reliable underthe particularly demanding use conditions of a motor-vehicle exhaustline.

Furthermore, from an energy standpoint, such devices are not verysatisfactory insofar as they in no way seek to decrease the energydedicated to the generation of the noise but, on the contrary, expend atleast an equivalent amount of additional energy.

Finally, these devices employ techniques for which the design of anexhaust line, fitted to such an engine and intended to be installed onsuch equipment, requires complex simulations of the behaviour of thefluid within the exhaust line, bearing in mind the elements of which itwill be composed, it being furthermore possible for these to be mutuallyinterfering.

It has also already been tried to damp the flow pulsations of a fluid ina pipe with the aid of variable-geometry devices which tend to modifythe resonant frequencies in the pipe by adapting the action of arestriction means to an overall measure of the flow rate of the fluid inthe pipe and not to the specific pulsations of the fluid.

The present invention aims to provide a novel inlet or exhaust linewhich does not have the drawbacks encountered in the known technique andwhich enables, in a substantial way, especially the sound level of acombustion engine to be attenuated, while at the same time being simpleand economical to produce.

In addition, the subject of the present invention turns out, due to itsstructure, to be remarkably suited to the various reciprocating machinesand to the various geometrical shapes that can be imposed on it.

The subject of the present invention is an inlet or exhaust line,especially for a reciprocating machine, characterized in that it isconstituted by a gas flow pipe, the said pipe being fitted with at leastone sensor for measuring a physical quantity characteristic of theinstantaneous flow rate of the gases, the exhaust line furthermoreincluding at least one device for variably restricting its cross-sectionfor passage of the gases, which instantaneously varies the energy lossof the gases flowing in the pipe as a function of the quantity measuredby the sensor, in order principally to reduce the low-frequencypulsations of the gases and the low-frequency components of the noisewhich result from its very presence in the gas duct, whereas theinternal wall of the pipe is lined with a material absorbing theacoustic energy in order principally to attenuate the high-frequencypulsations of the gases, as well as the high-frequency components of thenoise generated in the pipe by the restriction device.

Thus, the present invention combines the advantages of a variablerestriction device, which actively controls the flow pulsations of agas, with those of the lining of the walls of a pipe.

In fact, the inventors have noticed that these two devices, joinedtogether in one and the same inlet or exhaust line, enable noiseattenuations to be obtained which are better than those obtained byusing these devices separately.

The complementarity of the variable restriction device and of the liningof the internal wall of the pipe stems from the fact that the variablerestriction device, which constitutes an obstacle placed in the gasduct, is itself a noise generator.

Now, the sound level of this parasitic noise is limited to medium orhigh frequencies on account of the fact that, by construction, thevariable restriction device automatically eliminates the low-frequencypulsations of the gases, including those for which it could be thesource.

In contrast, the lining of the walls is relatively ineffective forattenuating the low-frequency noise but is particularly adapted to theattenuation of high-frequency noise.

Consequently, the lining of the walls is appropriate for eliminating thehigh-frequency noise of the gases, as well as the high-frequencycomponents of the noise generated by the active control device. Anotherrole of the lining is to avoid any significant reflection of theacoustic waves within the pipe.

In the case of a combustion engine, an exhaust line according to theinvention may dispense with silencers of the prior art.

According to one preferred embodiment of the invention, the device forrestricting the cross-section of the pipe acts on that part of the piperemote from the machine generating the pulsations.

In fact, it is preferable to actively control the pulsations of thegases as far as possible from the reciprocating machine, that is to sayby maintaining a large volume of fluid upstream of the restrictiondevice in order to avoid adversely affecting the energy efficiency ofthe said machine.

In another embodiment, the pipe portion located upstream of therestriction device possesses a diameter greater than that of the pipeportion which contains the latter. Thus, the pipe has a relatively largevolume, as in the preceding embodiment, thereby limiting theback-pressure generated during the restriction.

This arrangement may be useful in the case where such a line is to beinstalled in a confined place, for example at the outlet of an engine ofcertain vehicles or industrial engines.

An inlet or exhaust line according to the invention has, especially, theadvantage of occupying only a very small volume in comparison with theexhaust lines of the prior art.

This leads to a mass reduction since, in the absence of silencers, theweight of the inlet or exhaust line substantially comes down to theweight of the pipe.

These advantages are important for the motor-vehicle industry since thehousing of an exhaust line according to the invention and its attachmentbeneath a vehicle no longer raise the size and mass problems encounteredhitherto.

Being internally lined, the inlet or exhaust line according to theinvention furthermore has the following two advantages:

the risk of the wall of the pipe going into resonance with the gaspulsations is eliminated;

the radiated noise is also virtually zero since, on the one hand, theouter wall of the inlet or exhaust line is no longer subjected to thegas vibrations and, on the other hand, the emissive surface of the inletor exhaust line, that is to say its overall outer surface, isconsiderably reduced compared to that of a conventional exhaust linewhich is longer and includes silencers of large external diameter.

According to a particular embodiment of the invention, the inlet orexhaust line includes a means for regulating the restriction devicewhich causes attenuation of a preferential range of gas pulsationfrequencies enabling a particular sonority of the line to be obtained.

In this manner, it is possible to tune the "timbre" of the inlet orexhaust line as a function of the noise that is desired to be obtained.

For example, on a motor vehicle, the constructor or the purchaser of thevehicle may desire the exhaust line to emit either a noise with a sportyconnotation or a more attenuated noise.

With the same idea in mind, an industrial installation may emit a noisewith a disagreeable tone resulting from frequency combinations which,even at quite a low sound level, may be uncomfortable for the human ear.

By virtue of the inlet or exhaust line according to the invention, it ispossible to choose the frequencies to be attenuated by suitablyregulating the restriction device.

Moreover, according to one particular embodiment of the invention, theinlet or exhaust line equips a motor vehicle and its restriction deviceincorporates the speed of movement of the vehicle as an additionalparameter in order to attenuate as much as possible the exhaust noise ofthe engine when the vehicle is moving at low speed and in order tominimize the pressure drops of the exhaust gases so as to improve theperformance of the combustion engine when the vehicle is moving at highspeed.

It is understood that this embodiment is particularly advantageous foradapting the noise level of a vehicle used both in town, and thereforeat low speed, and on a main road or motorway, that is to say at highspeed.

According to another embodiment of the invention, the inlet or exhaustline includes an electronic device for analysing the signal output bythe measurement sensor with a view to detecting and possibly diagnosinga malfunction of the reciprocating machine.

In order to do this, it suffices for the said analysing device tocompare the various periods of the measured acoustic signal withreference signals.

For example, for a four-cylinder combustion engine, the perceivedacoustic signal has a cycle of four periods. An irregularity in one ofthese periods compared to the other three may reveal a malfunction ofone of the four cylinders.

For the purpose of making the invention easier to understand, twoembodiments of it will be described, these being given by way of exampleand in no way having a limiting character, with reference to theappended drawing in which:

FIG. 1 depicts an exhaust line according to a first embodiment of theinvention;

FIG. 2 depicts an exhaust line of the prior art;

FIG. 3 depicts an exhaust line according to a second embodiment of theinvention;

FIGS. 4 to 6 are graphs illustrating the differences in noise-reductioneffectiveness between the exhaust lines of FIGS. 2 and 3; and

FIG. 7 depicts a pressure measurement taken on an exhaust line accordingto the invention.

The wall 1a of the pipe 1 is made of metal and has a continuous smoothsurface.

Inside the pipe, a reticulated material 1b having wide meshes, such as ametal meshing, keeps a lining 2 pressed against the wall 1a of the pipe1.

By way of example, an exhaust line according to the invention has beenproduced which possesses an external diameter of 95 mm and a totallength of 0.60 m and which is internally lined with rock wool with athickness of 25 mm, this leaving an internal cross-section for passageof the exhaust gases of 45 mm in diameter.

The lining 2 is present from end to end of the pipe, save in thevicinity of a restriction device 3, the shutter 4 of which may be beenin the half-closed position.

A control member 5 controls the restriction device 3 as a function ofthe signal which it receives from a sensor 6 housed in the thickness ofthe pipe 1.

The operation of such a restriction device is described in the documentFR-A-2 613 089.

The pulsed gases output by the combustion engine flow into the exhaustline, as represented by the arrow 7.

It has been found that, because of its general shape, the exhaust lineaccording to the invention takes up little room and that it has aradiating surface area which is substantially reduced.

Furthermore, this exhaust line is by nature adaptable to any type ofengine, the matching of the restriction device being simply based on thefeedback-control law which it obeys.

From the industrial standpoint, this constitutes an advantage since themanufacturer of exhaust lines is not obliged to design and manufacturean exhaust line for each engine existing.

In FIG. 2, an exhaust line of the prior art has been depicteddiagrammatically. Such an exhaust line includes a pipe 8 45 mm indiameter mounted on the exhaust-gas outlet of an engine 9.

A catalytic converter 10, an expansion pot 11 and a silencer 12 aresuccessively arranged on the pipe 8 in the direction of passage of theexhaust gases.

An exhaust line according to a second embodiment of the invention hasbeen depicted in FIG. 3. This exhaust line has the same length as thatwhich has just been described.

However, the overall size of the exhaust line of FIG. 3 is less thanthat of the exhaust line of FIG. 2 because of the fact that the externaldiameters of the elements of which it is composed are smaller.

Beyond the catalytic converter 10, which fulfils the same function aspreviously, the expansion pot 11 and the silencer 12 of the prior arthave been replaced in this case by two lengths 13a and 13b provided withan absorbent material on their internal walls, these lengths beinglocated on either side of a variable restriction device constituted by avalve 14 of the throttle-valve type which is operated by an actuator 15,itself controlled by an electronic device 16 which analyses the dataoutput by two sensors 17a and 17b placed respectively on the engine 9and on the pipe 8, downstream of the valve 14.

The first length 13a provided with an absorbent material consists of apipe 0.8 m in length, internally lined with rock wool 20 mm in thicknesswhich is held in place by a meshing or a perforated metal sheet ofcylindrical shape and 45 mm in diameter.

The second length 13b equipped with an absorbent material has anidentical structure but has a length of 0.6 m.

The two exhaust lines of FIGS. 2 and 3 formed the subject of comparativetests, the results of which appear in FIGS. 4 to 6.

The sound levels of the noise of the exhaust lines were measuredidentically for each line, by placing a previously calibrated microphone10 cm from the plane of the outlet opening of each exhaust line and at45° to the axis of the latter.

The sound levels measured in a 20 to 20,000 Hz band, for speeds of theengine 9 varying from 1200 to 3800 revolutions per minute, gave the twocurves of FIG. 4, the upper curve 18 corresponding to the exhaust lineof FIG. 2 and the lower curve 19 corresponding to the exhaust line ofFIG. 3.

It is clearly seen in this FIG. 4 that the exhaust line of the prior artis substantially noisier than the exhaust line according to theinvention, whatever the speed of the engine 9.

Likewise, the performance of the two lines of FIGS. 2 and 3 werecompared using the technique called insertion-loss measurement: for eachexhaust line, a measurement was made in succession of the noise emittedby the exhaust line fitted with the element whose effectiveness it isdesired to measure, and then of the noise emitted by the said exhaustline whose element in question was replaced by a length of pipe equal inlength. The differences between the sound levels measured without thenoise-reduction element and those measured with the said element werethen plotted in the graphs of FIGS. 5 and 6.

Curves 20 and 22 correspond to the exhaust line of FIG. 3, while curves21 and 23 correspond to the exhaust line of FIG. 2.

FIG. 5 depicts the raw measurement expressed in decibels. In thisfigure, it is seen that the effectiveness of the exhaust line accordingto the invention is much superior to that of the exhaust line of theprior art.

In order to take into account the sensitivity of the human ear, the rawmeasurements of FIG. 5 were corrected using a known weighting technique,resulting in the curves depicted in FIG. 6 in which the unit of soundlevel is the decibel A (dB(A)).

In this FIG. 6, it is apparent that the difference in effectivenessbetween the exhaust line according to the invention and that of theprior art is great for all operating speeds of the engine 9.

FIG. 7 depicts a pressure measurement taken on the exhaust line of FIG.3, by virtue of the sensor 17b located immediately downstream of thevalve 14.

This pressure measurement corresponds to the operation of a 6-cylinderin-line engine running at a speed of 1300 revolutions per minute.

Each peak in the curve corresponds to the opening of the exhaust valvesof one cylinder.

The curve of FIG. 7 includes two cycles, each peak being denoted by anumber from 1 to 6, corresponding to the cylinder number in question.

In the present case, it may be deduced from this pressure measurementthat the cylinder 3 has a highly defective exhaust valve since there isno pressure drop between the peaks 2 and 3, which corresponds to anexhaust leakage at the moment of the pressure rise in the cylinder 3.

It may also be noticed that the cylinder 6 has a combustion defect sincethe pressure of the exhaust gases output by this cylinder is appreciablyless than that of the cylinders 1 to 5.

Although such a method of monitoring the correct operation of acombustion engine is known, the exhaust line according to the inventionenables this real-time method to be implemented when using the engine.

It is quite obvious that the embodiment which has just been describedhas no limiting character and that it may receive any desirablemodifications without departing thereby from the scope of the invention.

In a variant, a double wall could, in particular, be provided in orderto reduce the emissive capacity of the pipe substantially further.

Besides its application to any inlet or outlet nozzle of a reciprocatingmachine, the inlet or exhaust line according to the invention may beinserted into a pipe for gas or into a pipe for liquid or for a mixtureof both these phases, in which the inlet or exhaust line makes itpossible to attenuate the noise and the fluctuations in pressure and inflow rate which are generated by any more or less fortuitious orperiodic pressure wave propagating therein.

We claim:
 1. An exhaust line, especially for a reciprocating machine,comprising;a gas flow pipe fitted with at least one measurement sensorfor measuring a physical quantity characteristic of the instantaneousflow rate of the gases; the exhaust line further including at least onerestriction device for variably restricting a cross-section of theexhaust line and controlling passage of the gases, said at least onerestriction device instantaneously varying energy loss of the gasesflowing in the pipe as a function of the quantity measured by the atleast one measurement sensor in order to reduce low-frequency pulsationsof the gases and low-frequency components of noise which results fromthe presence of low frequency pulsations of gases in the exhaust line;an internal wall of the gas flow pipe lined with a material capable ofabsorbing the low frequency components of noise in order to attenuatehigh-frequency pulsations of the gases, as well as high-frequencycomponents of the noise generated in the pipe by the at least onerestriction device; the exhaust line further including an electronicdevice for analyzing the signal output by the at least one measurementsensor with a view to detecting and optionally diagnosing a malfunctionof the reciprocating machine.
 2. An exhaust line according to claim 1,wherein the at least one restriction device for restricting thecross-section of the pipe acts on a part of the pipe remote from thereciprocating machine.
 3. An exhaust line according to claim 1, whereina part of the pipe located upstream of the at least one restrictiondevice possesses a diameter greater than that of a part of the pipewhich contains the at least one restriction device.
 4. An exhaust lineaccording to claim 1, including a means for regulating the at least onerestriction device which causes attenuation of a preferential range ofgas pulsation frequencies enabling a particular sonority of the exhaustline to be obtained.
 5. An exhaust line, especially for a reciprocatingmachine, comprising;a gas flow pipe fitted with at least one measurementsensor for measuring a physical quantity characteristic of theinstantaneous flow rate of the gases; the exhaust line further includingat least one restriction device for variably restricting a cross-sectionof the exhaust line and controlling passage of the gases, said at leastone restriction device instantaneously varying energy loss of the gasesflowing in the pipe as a function of the quantity measured by the atleast one measurement sensor, in order to reduce low-frequencypulsations of the gases and low-frequency components of noise whichresults from the presence of low frequency pulsation of gases in theexhaust line; an internal wall of the gas flow pipe lined with amaterial capable of absorbing the low frequency component of noise inorder to attenuate high-frequency pulsations of the gases, as well ashigh-frequency components of the noise generated in the pipe by therestriction device; the exhaust line equipping a motor vehicle, and theat least one restriction device incorporating the speed of movement ofthe vehicle as an additional parameter in order to attenuate as much aspossible the exhaust noise of the engine when the vehicle is moving atlow speed and in order to minimize the pressure drops of the exhaustgases, so as to improve the performance of the combustion engine whenthe vehicle is moving at high speed.
 6. An exhaust line according toclaim 5, wherein the at least one restriction device for restricting thecross-section of the pipe acts on a part of the pipe remote from thereciprocating machine.
 7. An exhaust line according to claim 5, whereina part of the gas flow pipe located upstream of the at least onerestriction device possesses a diameter greater than that of a part ofthe pipe which contains the at least one restriction device.
 8. Anexhaust line according to claim 5, including a means for regulating theat least one restriction device which causes attenuation of apreferential range of gas pulsation frequencies enabling a particularsonority of the exhaust line to be obtained.